1. Technical Field
The present invention is related to preservation of red blood cells in substantially physiologically native state. More particularly, the present invention is related to a novel suspension medium for storage of human red blood cells at about 4.degree. C. in a condition suitable for blood transfusion. The novel suspension medium of the present invention makes it feasible to substantially increase the storage time of the red blood cells than was heretofore possible.
2. Prior Art
Storage or preservation of red blood cells in a suspension medium at about 4.degree. C. according to standard blood bank procedure is well known. As far as known to the Applicants there are no literature references reporting the effects of either of hypotonic suspension or of the additon of penetrating salts, e.g., ammonium salts as related to the keeping quality of red blood cells.
It has been observed, however, that, during continued refrigerated storage, human red cells undergo a shape change with the development of spicules which may ultimately bud off into small vesicles. This reduces the surface area of the red cell, presumably rendering it less flexible and less able to pass through the filtration system in the spleen. This in turn leads to the removal of cells from the circulation within a few minutes following transfusion. Acceptable standards for transfusable red cells require that at least 70% of the cells must still be circulating 24 hours following transfusion.
The present invention overcomes the limitations and problems associated with the prior art process. It was reasoned that increasing the surface tension of the cells by osmotic swelling would theoretically tend to forestall the development of spicules. Therefore, a suspension medium of suitable osmolarity and membrane permeability was developed which could preserve the red blood cells at 4.degree. C. for extended period of time in a condition suitable for transfusion in accordance with standards established for transfusion of red blood cells (RBCs). It was discovered that inclusion of certain penetrating compounds, such as ammonium salts, preferably NH.sub.4 Cl and NH.sub.4 COOCH.sub.3, in a suspension medium not only avoids the deleterious effects of low ionic concentration, but also provides certain positive benefits as described more fully infra.